1. Field of the Invention
This invention relates in general to a recording head for recording or printing images such as characters and graphical representations, by applying an electric current to a recording medium or a ribbon or film or other form of intermediate member interposed between the recording medium and the recording head. More particularly, the present invention is concerned with construction of a distal end portion of such a recording head at which the head contacts the recording medium or intermediate member to perform high-quality recording.
2. Discussion of the Prior Art
Various types of recording heads for recording by application of an electric current to a recording medium or an intermediate member have been proposed up to the present. In particular, there is known a recording head having a laminar or multi-layered structure which includes an electrically insulating layer or layers, an array of recording electrodes and an array of return circuit electrodes which are supported by or formed on the insulating layer or layers. Examples of this type of recording head are disclosed in laid-open Publication Nos. 61-35972, 62-292461, 54-141140, 58-12790 and 61-230966 of unexamined Japanese Patent Applications.
As disclosed in the publications identified above, the recording head of the type indicated above is adapted such that an electric current is applied to an electrically resistive or conductive layer formed or coated on or carried by a suitable recording medium or a suitable planar intermediate support member in the form of a sheet, film, or ribbon. The electrically resistive or conductive layer may be formed on a roller or other support member, or constitute an inner layer of the recording medium or support member. During recording by using, for example intermediate ribbon or film having an electrically resistive layer and an ink layer, an electric current applied to the resistive layer through the recording head causes Joule heat to be generated by the resistive layer, whereby selected local areas of the ink layer are heated, and the ink material in these heated local areas is fused, vaporized or diffused. As a result, the ink material is transferred to the appropriate local areas of the recording medium so as to form a black or colored image. If an electric current is applied directly to a recording medium, the appropriate local areas of the medium are suitably colored due to Joule heat generated by an electric current, or due to removal of the covering material from the medium surface due to an electrical discharge occurring thereon.
The electrically resistive layer provided on the recording medium or intermediate support member may be an electrically conductive layer, an electrically conductive or resistive ink layer (which serves also as an ink-bearing layer), a heat-sensitive layer having an electrolyte, or any form of layer through which an electric current may flow.
During recording or printing operation by the recording head as described above, the recording electrodes and the return circuit electrodes must be constantly held in good electrical contact with the electrically resistive layer of the recording medium or support member. In the known recording heads of a laminar structure having recording and return circuit electrodes and the electrically insulating layer interposed therebetween, the materials, dimensions and arrangement of the electrodes, insulating layer and other elements are optimally determined so as to assure good electrical contact of the electrodes with the resistive layer.
However, the mere selection of the materials suitable for the electrodes, insulating layer and others, and appropriate dimensions and arrangement thereof are not sufficient for maintaining good and stable electrical contact of each electrode with the resistive layer for a prolonged period of time. Consequently, it is difficult for the known recording heads to provide high-quality printed images having small variation in their density.